VARIATION 411 



as that which gave rise to the copper-heech in the 16th cen- 

 tury, or to hornless cattle, or to short-legged sheep, or to 

 Angora rabbits, or to fantail pigeons. They correspond to 

 Galton's " transilient variations ", to Bateson's " discontinu- 

 ous variations ", to De Vries's " mutations ", and the last 

 name should be kept for them. The contrast, it should be 

 noted, is not so much in the amount as in the kind of change. 

 A white rat does not seem to lack very much to make it a 

 brown rat the species whence it sprang, but it was in its 

 day a qualitative new departure, and it has bred true, (b) 

 By " individual variations ' Darwin meant the minute, 

 ubiquitous peculiarities which distinguish child from parent, 

 brother from brother, cousin from cousin. Though he was 

 much interested in the " single variations ' or brusque 

 " sports ", it was in " individual variations ' or minute 

 fluctuations that he found most of the raw materials of new 

 species. " The more I work," he said, " the more I feel 

 convinced it is by the accumulation of such extremely slight 

 variations that new species arise." 



Some authors have tried to identify Darwin's slight in- 

 dividual variations or fluctuations with the somatic modi- 

 fications already referred to. While this may be sometimes 

 justified in point of fact, Darwin did not regard minute 

 variations as modificational. This is plain from such a 

 sentence as this: "If, as I must think, external conditions 

 produce little direct effect, what the devil determines each 

 particular variation ? ' Moreover, fluctuations or minute 

 variations often arise among animals whose conditions of 

 life appear to be quite uniform. On the other hand, what 

 Johanssen calls fluctuations in " pure lines ' of beans are 

 probably slight modifications due to differences in nurture. 



Little is known in regard to the transmissibility of 



